Photo-electric tube



Aug. 9, 1932- H. c. RENTSCHLER y-- PHOTO-ELECTRIC TUBE Filed Feb. 17. .1930

INVENTOR ATTORNEY atented Ange HARVEY CLAYTON BENTSCHLER, OF EAST ORANGE, NEW JERSEY,

ASSIGNOB TO WEST INGHOUSE LAMP COMPANY, A CORPORATIQN OF PENNSYLV i k l PHOTO-ELEGTRIG TUBE Application filed February 17, 1930. Serial No. 4283M.

This invention relates to photoelectric tubes sensitive to the ultraviolet and visible but more particularly to the ultraviolet region of the spectrum.

Photo-electric tubes in common use for measuring or detecting radiations employ a photo sensitive material on the cathode, usually an alkali metal, zinc or cadmium. Thorium, misch metal and uranium may also be used in measuring ultraviolet radiations of a particular ran e of wave lengths.

One of the o jects of the present invention is to produce a photoelectric tube which is sensitive to radiations from about 5500 Angstroms into the ultraviolet,

Another object of this invention is to provide a photoelectric tube which is sensitive to radiations throughout the whole ultraviolet range and in which the photo-electric efl'ect will be strong.

Other objects and advantages will hereinafter appear.

According to my invention I provide a photo-electric tube having a nickel or iron anode and a lithium cathode in an envelope preferably composed of a boro silicate glass free from iron commonly known in the art under the trade name Corex glass. The lithium cathode is deposited on a coating of noble metal which is also deposited on the envelope so as to keep the lithium at all times out of contact with the envelope.

Many attempts have previously been made to produce a practical tube which employs lithium as the photo-sensitive material but because of the reaction which takes place between lithium and glass the metal surface has been destroyed.

reference is made to the accompanying drawin in which ig. 1 is an elevational view partly in section of a photoelectric tube embodying my invention;

Fig. 2 is an elevational view partly in secthe method described below. For a better understanding of my invention tion of the photoelectric tube shown in Fig 1, the figure being taken at 90 and in an inverted position relative to the position shown in Fig. 1,;

Fig. 3 is a perspective view of the carrier for the photo-sensitive material. 7

The photo-electric tube shown in Figs. 1 and 2 comprises an envelope 10 having a cathode 11 and an anode 12 therein. The anode consists of a metal frame comprising two parallel uprights 13 and 14 and a bracing cross member 15. The upright member 13 and 14 are sealed in the press 16 of the tube. The anode 12 is preferably composed of iron or nickel.

The cathode 11 comprises a thin coating of lithium deposited on a coating of gold, platinum or silver which is adhered to the inner surface of the envelope 10. This coating of gold, for example, may be applied by painting the surface of the glass with a commerclal preparation known as liquid bright gold, drying for a few minutes at about 150 C. and then baking for 10 to 15 minutes at a temperature of around 500 C. Durin baking a stream of air should be maintained through the bulb to carry away the volatilized material given ofi from the coating.

- The gold is deposited over a considerable area of the bulb interior. Prior to depositing the gold on the bulb a terminal 17 is at tached to the envelope 10 and connected to the interior of the bulb by a wire 18 sealed through the side wall of the envelope. The gold coating then adheres closely to the wire 18 forming a good contact therewith. Lithium is then deposited on the gold coating by A movable carrier for the lithium, preferably in the form of a pellet 20 consisting of about one part of lithium fluoride and ten parts of mlsch metal filin s, is mounted in the plate. 21 of slider 19 w ich slides on the anode 12.

This carrier may take a variety of forms but should be of such form that it can be readily heated by high frequency currents y from the exterior of the envelope. As illustrated the carrier comprises a hollow tubular 5 plate member 19 disposed about the anode 12 so that it may be readily slid from one.

end to the other thereof, and has welded on one face thereof a struck out plate 21 to form a ocket in which a ellet containing a 10 lit ium compound and a reducing agent may be wedged.

In the manufacture of the tube the cathode lead wire is sealed in the wall of the envelope, the gold coating is deposited on the envelope 5 and the anode mount with the carrier and pellet assembled thereon is also sealed to the tube. The tube is then baked out and exhausted with the tube positioned as shown in Fi 2. The carrier 19, as shown in full line is heated by a high frequency induction coil placed about the envelope. This heating is continued until an appreciable layer of lith-' ium has been reduced from its compound in the pellet and deposited on the gold coating. The carrier is preferably so arranged within the tube that the lithium is deposited only on-the center portion of the gold coating. The tube is now sealed ofi.

After the cathode has been formed the lithium carrier is moved to the position shown in full lines in Fig. land in dotted lines in Fig. 2 by invertin the tube.

' The envelope 10 must e composed of a glass which is transparent to light in the desired region. Preferably I use Oorex I glass which is substantially transparent to ultraviolet.

In order to further decrease the absorption of ultraviolet light in the glass a thin window 22 may be formed in the envelope oposite the cathode 11.; The window 22 is ormed by heating a portion of the envelope and drawing-in such portion to form a reentrant bulbous body having a thin dome.

Such a window increases the current output of the tube very greatly, particularly in the lower wave length regions of the spectrum. If desired a gaseous filling of a rare gas, such as argon, neon or helium at a suitable pressure may be employed.

Instead of the lithium fluoride compound in the ellet 20 I may use another lithium salt and may em 10 a difi'erent reducing agent instead of 111180 metal, if desired.

A photoelectric tube produced in accordance with my invention is sensitive to light in the blue end of the visible spectrum, the photoelectric efi'ect starting in about the green region thereof, and extending through the ultraviolet.

It is to be understood'that many changes may be made in the construction of the tube without departing from the invention and I do not desire to be limited except in accordance with the appended claim.

' uanvn CLAYTON namscmra. 

